The present invention generally relates to scanning systems, and more particularly to a telecentric illumination scanning system for illuminating a liquid crystal valve.
One current technique for illuminating liquid crystal light valve based projection systems, used by an affiliate and assignee of the present invention, is a continuous full frame, full aperture illumination system, wherein light is relayed or directed to a light valve in a telecentric or near-telecentric manner. The light valve is activated by writing a video frame one line at a time on the back of the light valve (for a reflective photoconductive light valve) or in pixel blocks (e.g. 64 at a time) for a matrix type transmissive or reflective light valve.
Prior art systems include refractive scanning systems in which several cylindrical lenses are placed around the periphery of a disk and thereby scan by bending the light path. Each lens covers a percentage of the light valve depending upon the number of lenses, or the shape of the refractive surface (i.e., one continuous lens as opposed to multiple lenslets). This approach is very sensitive to eccentricity of rotation. Another approach incorporates a refractive cube that rotates about an axis perpendicular to transparent cube faces. This approach uses a well-known principle of axis displacement due to a tilted parallel plate. In accordance with this principle ##EQU1## where t is the thickness of the plate or cube, .theta. is the angle tilted, and n is the index of refraction of the plate or cube. Both approaches are sensitive to chromatic effects, and other aberrations. With the cube approach the aberrations of all rays (that is, the cone rays), other than chief rays, vary as the angle varies in rotation.
Accordingly, it is an objective of the present invention to provide for a telecentric illumination scanning system for illuminating liquid crystal light valves that overcomes the limitations of the prior art scanning systems.